PURPOSE: To obtain correct measurement results in a short time with a simple structure by alternately applying potential for electrolytically oxidizing electrochemical active species and potential for electrolytically reducing the same to a working electrode and making quantitative measurement based on a secular change rate of measured signals.

CONSTITUTION: A matrix which produces electrochemical active species which can be electrolytically oxidized and reduced repetitively by reaction with enzymes to be quantitatively measured is with the enzyme wherein a potential at which the produced electrochemical active species are electrolytically oxidized and a potential at which they are electrolytically reduced are alternately applied to a working electrode to obtain a signal derived from the amount of the active species, and a secular change rate of the signal is calculated, based on which quantitative measurement is made. By thus applying the potential for electrolytically oxidizing and the potential for electrolytically reducing to the working electrode alternately, it is possible to quantitative measure the enzyme by the secular change of the measured signal without irreversibly consuming reaction product produced by the enzyme reaction so that correct measurement results can be obtained in a short time with a simple structure.